The invention relates to a torsional vibration damper with flange sleeves for guiding a rotating ring in a damper housing, the flange sleeves guiding the rotating ring with respect to the damper housing and being inserted loosely, that is, without prestress, between the housing and the ring, and simultaneously maintaining defined shearing gaps between the housing and the ring.
The shearing gap damper, traditionally called a visco or torsional vibration damper, is usually flanged at an output side of diesel engine crankshafts with respect to the power and reduces their torsional vibration amplitudes. As a result of an oscillating shearing of the silicone oil damping medium in the interior of the damper, the oscillation energy is converted to heat which, as a result of convection, is conveyed to the ambient air or to another cooling medium.
Shearing gap dampers normally consist of a ring-shaped housing (1 in FIG. 1) which encloses a secondary mass 2 called a “rotating ring”. The housing is connected with the crankshaft M in a torsion-proof manner.
The damper housing and the rotating ring follow the mean rotational speed of the crankshaft without any slip. In contrast, their torsional vibrations, which are superimposed on the uniform rotation, are first communicated only to the housing. The rotating ring would rotate in a uniform manner if it were not coupled to the housing by the damping medium which fills the narrow shearing gap 3. This coupling is elastic and subject to damping. As a result, relative angles of rotation of an angular degree of up to ±1° in time with the exciting oscillations occur between the housing and the rotating ring.
Since the rotating ring can therefore rotate in an oscillating manner with respect to the housing, it requires guiding elements.
From European Patent Document EP-PS 0 745 784 B1, a rotating ring bearing in the manner of a “flange sleeve” is known which is made of plastic and has an L-shaped cross-section. A pair of such flange sleeves are part of the equipment of a shearing gap damper. These flange sleeves are inserted without prestress, that is, loosely between the housing and the ring, so that, during relative movements, both metal parts slide on the flange sleeve with the smallest possible coefficient of friction.
The flange sleeves according to European Patent Document EP-PS 0 745 784 B1 provide the best conditions for an uncomplicated fully automatic assembly of shearing gap dampers. However, it was found that the flange sleeves did not yet meet all requirements of an economical manufacturing.
In particular, the closed angle rings according to European Patent Document EP-PS 0 745 784 B1 are not optimal with respect to the excessively different linear coefficients of thermal expansion of the participating materials:
Steelα = 0.0115 mm/(m × ° C.)cast ironα = 0.0105 mm/(m × ° C.)PA 66 α = 0.070 mm/(m × ° C.)PTFE α = 0.130 mm/(m × ° C.)
According to the temperature range to be assumed—from an arctic −50° C. through +20° C. during the assembly, to +100° C. in the engine, plastic rings grow with, for example, 160 mm bearing diameter by ΔI=5 to 9 mm in comparison to the housing and rotating ring. Such an increase in length would not take place without any constraints or compression of the bushing cross-section and cannot be accepted.
The straight or diagonally slotted butt joint of the flange sleeves according to European Patent Document EP-PS 0 745 784 was sufficiently wide for easily compensating the temperature-caused length increase of the plastic material. However, the incompatible instability of the cut-open angle rings was a disadvantage. They interlocked and deformed during transport and resisted the grippers of the assembling devices.
It is an object of the present invention to provide a torsional vibration damper of this type, which has a flange sleeve as a bearing device, in such a manner that it accomplishes the required length compensation and, simultaneously, is sufficiently dimensionally stable in order to be able to be processed by a fully automatic production facility.
The invention achieves this task by providing a viscosity-type torsional vibration damper with flange sleeves for guiding a rotating ring in a damper housing, the flange sleeves guiding the rotating ring with respect to the damper housing and being inserted loosely, that is, without prestress, between the housing and the ring, and simultaneously maintaining defined shearing gaps between the housing and the ring. The flange sleeves are formed of a plastic material, and have a preferably L-shaped cross-section, as well as having a butt joint at one point of the circumference. The butt joint is bridged by at least one or more material webs. Accordingly, the butt joint is bridged by at least one or more material webs which, however, do not extend along the above-mentioned width of the flange sleeve.
In a simple manner, the material webs permit good storage properties and easy transportability of the flange sleeves, and also decisively facilitate assembly because deformation and warpage of the slotted rings is prevented.
Advantageous further developments of the invention are described herein.
Essentially two types of approaches present themselves. The butt gap of the flange sleeve is bridged by webs which                break at the operating temperature, or        deform in an elastic-plastic manner at the operating temperature.        
The flange sleeves are preferably L-shaped. However, the invention is theoretically also suitable for slotted plane axial or radial bearing rings.